Latent prints

Although the word latent means hidden or invisible, in modern usage for forensic science the term latent prints means any chance or accidental impression left by friction ridge skin on a surface, regardless of whether it is visible or invisible at the time of deposition. Electronic, chemical and physical processing techniques permit visualization of invisible latent print residue whether they are from natural secretions of the eccrine glands present on friction ridge skin (which produce palmar sweat consisting primarily of water with various salts and organic compounds in solution), or whether the impression is in a contaminant such as motor oil, blood, paint, ink, etc.

Latent prints may exhibit only a small portion of the surface of the finger and may be smudged, distorted, or both, depending on how they were deposited. For these reasons, latent prints are an “inevitable source of error in making comparisons,” as they generally “contain less clarity, less content, and less undistorted information than a fingerprint taken under controlled conditions, and much, much less detail compared to the actual patterns of ridges and grooves of a finger.”

Patent prints

These are friction ridge impressions of unknown origin which are obvious to the human eye and are caused by a transfer of foreign material on the finger, onto a surface. Because they are already visible they need no enhancement, and are generally photographed instead of being lifted in the same manner as latent prints. Finger deposits can include materials such as ink, dirt, or blood onto a surface.

Plastic prints

A plastic print is a friction ridge impression from a finger or palm (or toe/foot) deposited in a material that retains the shape of the ridge detail. Commonly encountered examples are melted candle wax, putty removed from the perimeter of window panes and thick grease deposits on car parts. Such prints are already visible and need no enhancement, but investigators must not overlook the potential that invisible latent prints deposited by accomplices may also be on such surfaces. After photographically recording such prints, attempts should be made to develop other non- plastic impressions deposited at natural/